1. Field of the Invention
The present disclosure pertains to a method and an apparatus for controlling pressure during enhanced cough flow of a subject.
2. Description of the Related Art
Several respiratory diseases, such as Chronic Obstructive Pulmonary Disease (COPD), Asthma, Cystic Fibrosis (CF), etc., are characterized by an accumulation of fluid or viscoelastic material, i.e., mucus or secretions, in the respiratory system of a patient. An increase amount of mucus (due to hypersecretion and/or reduced ability to clear secretions from the lung) in the respiratory system is often associated with respiratory difficulties, and may lead to complete blockage of gas alveoli of the respiratory system. The clinical consequences of hypersecretion are impaired gas exchange and compromised mucus clearance, increasing bacterial colonization and associated exacerbations. Excess of secretion may be cleared through cough or expectorating phlegm from the throat.
A natural phenomenon to expel such lung mucus is coughing. Cough consists of an inspiratory phase, closure of glottis, a build-up of pressure in the lung by muscle contraction, followed by an expiratory phase at which the glottis is opened, resulting in airflows with high velocity that are intended to pick up any material residing on the airway wall and propel it upwards towards the mouth. In numerous situations, natural cough is insufficient to expectorate these secretions. For example, cough remains ineffective due to inability to generate sufficient cough flow, abnormal properties of secretions in the lung, or a combination of both. In a number of respiratory diseases, the inability to develop airflow has to do with collapse of the airways during the cough manoeuvre.
Assistance means to help a patient expectorate secretions have been developed. For example, various systems for increasing patient cough flow through mechanical insufflation and exsufflation are known. Conventional exsufflation is generally accomplished using a single exsufflation event over a single exhalation of the subject. A respiratory circuit may be pressurized by a device, after which device applies negative pressure to the airways, causing high expiratory flows. Secretions built up in the airway of the subject over time may be expelled with the gas.
Another system for increasing patient cough flow, for example, use a passive variable flow resistor aimed at generating pressure oscillations during exhalation such that a single cough is segmented into multiple mini-coughs by intermittently opening and closing of a valve positioned in the expiratory air path. For example, such a system is configured to periodically obstruct cough flow, periodically increase pressure in the airways during cough, and allow airways to remain open and cough volume to be maximized. In such a system, when the valve closes, the pressure in the lung or respiratory system may rapidly rise due to continued muscle contraction during the cough and, when the valve opens, the lung pressure may rapidly drop to near ambient pressures.